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Case Files - Black Widow Spider Envenomation

Black widow spider on web
Toxicology Case Files from the Utah Poison Control Center
Teaching Points
  • Black widow spider envenomation may cause both local and systemic symptoms including pain, muscle cramping, sweating and gastrointestinal upset.
  • Treatment of mild to moderate envenomation is with enteral and parenteral analgesics and anxiolytics such as benzodiazepines.
  • Treatment of severe envenomation (refractory symptoms or elevated blood pressure, myocardial infarction or rhabdomyolysis) is with equine derived black widow spider antivenom. 
Case Presentation

A 45 year old male presented to the Emergency Dept (ED) early in the morning with leg pain. He had found a spider in his bed which was identified as a Black widow (BWS). The pain began in his upper leg but had spread into his chest and back. On exam he had what appeared to be a small bite mark in his thigh with a small amount of surrounding erythema. His vital signs were notable for hypertension and were otherwise normal.

In the ED the patient was initially given low doses of hydromorphone and midazolam. His symptoms did not improve and ketorolac, acetaminophen and ketamine were also administered. After this, and in spite of increasing doses of intravenous opioid and benzodiazepine medications, his symptoms persisted and he complained of severe chest and back pain with increasing blood pressure measurements. His creatine kinase (CK) was noted to be mildly elevated but his EKG was reassuring and troponin was normal.

Due to persistent and worsening symptoms the patient required admission to the hospital. Shortly after admission to the hospital, the patient received treatment with BWS antivenom and his symptoms abruptly improved. He was able to be discharged from the hospital in good condition several hours later.

Black widow spider envenomation

Black widow spiders (Latrodectus mactans) are found in every US state except Alaska. There are several species of venomous widow spiders in the US and not all have the red hourglass on the ventral abdomen that is typical of Latrodectus mactans. BWS venom contains alpha-latrotoxin which causes opening of cation channels, Ca2+ influx and massive release of acetylcholine, dopamine, norepinephrine and other neurotransmitters, leading to the clinical syndrome known as latrodectism.

BWS bite itself is described as a pinprick and often occurs after a web is disturbed or on inadvertent exposure in clothing or shoes. The bite may show a small puncture wound and occasionally a surrounding halo. Symptom onset is 30 minutes to a few hours and symptoms may last for several days. Symptoms generally progress contiguously from the site of the envenomation. Many patients will have mild pain near the bite site and normal vital signs (mild envenomation) with little or no progression of symptoms. Severe symptoms can include generalized pain especially in the chest, back and abdomen, with associated nausea and vomiting, headache and diaphoresis. Muscle cramping and rhabdomyolysis may occur and life-threatening reactions including severe hypertension, myocardial infarction and cardiovascular failure have been reported. Death from BWS envenomation has not occurred.

Management of BWS Envenomation

Treatment of mild to moderate envenomation is supportive with benzodiazepines and opioid or non-opioid analgesics, and many patients are able to be managed at home with or without a short course (2-3 days) of enteral opioids. Current evidence does not support the use of calcium or other adjuncts for treatment. Patients who are refractory to multiple doses of benzodiazepines and opioids in the ED, or who have other evidence of severe envenoming (severe range hypertension, elevated troponin or CK) may be treated with black widow spider antivenom. The current preparation of antivenom is equine derived, confers some risk of anaphylaxis, and there are extremely rare reports of death after administration. Patients with a history of anaphylaxis or asthma should not receive the antivenom. Any patient receiving antivenom should be closely monitored for evidence of anaphylaxis. Equine-derived antivenom is available in limited supply and providers should consider checking their hospital stock early when managing a patient with BWS envenomation. A newer sheep derived antivenom which is not yet available in the United States may ameliorate some of these issues.

Disposition and Sequelae

Recovery after BWS envenomation is expected to be complete within a few days with no long-term sequelae.

Call the poison control center at 1-800-222-1222 for assistance in managing black widow spider envenomation.

  1. Repplinger DJ, Hahn IH. Arthropods. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank's Toxicologic Emergencies, 11e. McGraw Hill. 2019: 1540-1558.
Author: Alyrene Dorey, MD; Assistant Professor, Emergency Medicine; Assistant Medical Director, Utah Poison Control Center; Medical Toxicology, University of Utah and Primary Children's Hospitals